Chemical composition and process



2,909,412 CHEMICAL COMPOSITIGN AND PROCESS Cletus E. Peeler, Jr., Dallas, Tern, assiguor to Diamond Alkali Company, Cleveland, Ohio, a corporation of Delaware i No Drawing. Application November 22, 1954 Serial No. 470,538

6 Claims. (Cl. 23-230) This invention relates to improvements in the manufacture of water-soluble alkali metal silicates and to improvements in the properties of such silicates.

Alkali metal silicates, such as sodium metasilicate, are well known and have found extensive utility in various washing and cleansing arts, either alone or combined with other substances having properties complementary to the desirable characteristics of the silicates. The silicates having Na O:SiO ratios of approximately 1:1 or higher are particularly useful in View of their increased alkali content.

Reference hereinafter will frequently be made to sodium metasilicate and its hydrates as typical commercially useful products. However, the present invention is concerned with alkali metal silicates generally and is not limited to sodium metasilicate, although it is recognized that the sodium silicates constitute the most widely used siliceous materials.

Perhaps the most common method of manufacturing sodium metasilicate involves the causticization of ordinary liquid sodium silicate, thereafter, if necessary, treating this liquid with caustic soda (76% Na O) to produce the desired alkali-silica ratio, and subsequently crystallizing the rrietasilicate by stirring, cooling, and seeding, as necessary. When a rise in temperature occurs, indicating inc-ipent crystallization, the reaction mixture is cast into pans or molds, where it harderis and may be ground to the desired particle size. n

However, as prepared" in the above-described manner, or in other commercial processes, sodium silicates generally are subject to serious disabilities which heretofore not only have limited their commercial attractiveness, but in some instances have definitely restricted their use. Perhaps the most objectionable disability, particularly in the case of sodium metasilicate pentahydrate, is its relatively poor shelf life, in that Within periods as short as a few weeks, silicates which, when originally manufactured were pure white, assume a discoloration, usually a yellowing. This discoloration darkens over a period of from aboutthree to six months, detracting from their appearance and rendering the silicates unusable in many applications. Such discoloration is particularly disadvantageous in those applications Where the white sodium metasilicate product is required, as when it is compounded with various other washing or cleansing compounds.

The present invention has as its principal object the provision of alkali metal silicates having improved properties over prior art compositions of similar character and function.

A further object of this invention is the provision of methods of preparing such silicates which preclude the disadvantageous discoloration heretofore encountered.

A still further object is the provision of methods of testing alkali metal silicates and compositions of matter useful in the practice of such methods.

These and other objects and advantages of the present invention will appear more fully from the following description.

The practice .of the present invention contemplates contacting an alkali metal silicate with a source of at least one transitional element, the resultant color of the silicate indicating an alkaline or siliceous Na O:SiO ratio and whether sufficient impurities are present to cause ultimate discoloration of the silicate. As used in the specification and claims herein, the expression transitional element -is intended to include the metals scandium, titanium, vanadium, chromium, manganese, iron,

cobalt, and nickel, as indicated in Mellors Inorganic Chemistry, 1952 ed., at page 870. These metals may be further characterized as having less than ten electrons in the 3d orbital, as shown on pages 98-99 of Mellor. While sources of any of the foregoing metals may be used, it will be recognized that sources of chromium, manganese, iron, cobalt, and nickel generally are relatively inexpensive and more readily available. Ac-

cordingly, particular reference hereinafter will be made to these metals.

The present invention contemplates that the alkali portion of the silicate compositions under consideration may be any of the alkali metals, including lithium, sodium, potassium, rubidium, and cesium, although, as indicated hereinbefore, the recognized commercial compounds are usually sodium silicates. Moreover, except where otherwise indicated, reference will be made to the sodium metasilicate ratio material, as this material is normally of major commercial interest and heretofore frequently has exhibited the most pronounced ultimate discoloration. In carrying out the practice of this invention, a quantity of aqueous sodium metasilicate liquor to be tested is contacted with a minor amount of at least one transitional element. The thus-formed mixture is allowed to crystallize and harden. Its color is indicative of the alkali-silica ratio and impurity content. Depending upon the color exhibited, alkali or silica corrections, or fur ther purification of the silicate, if necessary, can be accomplished.

In some instances, even more advantageous results are obtained by contacting a silicate liquor with a mixture of compounds of these elements, a mixture of compounds of iron and cobalt in known proportions being particularly useful in this respect.

As sources of the foregoing metals, generally their compounds which are compatible with the silicate material and soluble therein may be used. However, it is preferred to employ a neutral compound to avoid any undesired alteration of the alkali-silica ratio in the material being treated. Illustrative of satisfactory compounds which may be employed are halides, the chlorides and bromides being preferred, nitrates, sulfates, and thiocyanates. It will be understod, of course, that compounds of the metals 'in which the metals have varying valences are included among those which may be employed. For example, cobaltous and cobaltic compounds and/ or ferric and ferrous compounds may be used. In addition to the aforementioned compounds, various complex salts may be used, any such complex salt, such as complex iron salts, for example, preferably meeting the requirements of neutrality, compatibility, and solubility in the metasilicate. While any of the aforementioned compounds may be employed, in testing sodium metasilicate pentahydrate liquors, it is preferred to use a to the degree of hydration. Hence, in working with the, nine hydrate it is advantageous to double the amount of 3 cobalt acetate used in testing the pentahydrate. In many instances, optimum results are obtained using, in combinaton with a cobalt salt, an iron compound, either ferrous or ferric. While generally any iron and cobalt compounds meeting the hereinbefore prescribed requirements may be employed, it has been found that cobaltous acetate and its hydrates, particularly the tetrahydrate, alone, or in combination with a compound selected from the group of ferrous acetate and ferrous sulfate, is preferred.

The practice of this invention provides a rapid, sharplydefined color change indicative of the critical meta ratio and the presence of impurities in amounts suflicient to cause subsequent discoloration of the silicate. It will be understood that the metallic color indicator of this invention also is useful in determining the variation of a particular metasilicate liquor from the true metasilicate ratio. By comparison of the developed color with predetermined standards, by comparison with untreated samples from the same batch of silicate, or preferably by conducting one or more tests in which an amount of alkali, e.g., sodium hydroxide, sufficient to alter the Na O:SiO ratio by a predetermined amount is added, the alkalinity or siliceousness may be accurately determined.

The presently preferred practice of this invention in testing evaporated metasilicate liquors involves weighing two Samples of the liquor having a specific gravity within the range from 61-63 B. at 100 C., cooling these samples to 650 C., adjusting one sample with sodium hydroxide to a known alkali-silica ratio differential of 0.015 Na O (or other predetermined amount) and adding minor amounts of cobalt and iron solutions to both samples. The silicates are then crystallized and cast on flat glass plates for color observation. It will thus be appreciated that the present invention provide an extremely valuable process control. The practice of this invention, unlike convential analytical procedures, permits the rapid, accurate evaluation of silicate liquors, thereby facilitating frequent checking of product quality. It will be appreciated by those skilled in the art that while reference herein is made to various silicate liquors, anhydrous silicates may be tested readily merely by dissolving a portion of the silicate in water to form a crystallizable material.

In order that those skilled in the art may more completely understand the present invention and the preferred methods by which the same may be carried into effect, the following specific examples are offered:

EXAMPLE I Part A Into each of two 400 ml. beakers are weighed exactly 300 gms. of a sodium metasilicate pentahydrate liquor, having a specific gravity of 6l63 B. at 100 C., to be tested. Into one of the beakers, the contents of which are first cooled to 65 C., are added 4 ml. of a 10% aqueous cobaltous acetate solution and 1 ml. of a 10% aqueous ferric sulfate solution. The resultant mixture is stirred thoroughly and, when a 2 C. temperature rise indicates incipient crystallization, is poured out to harden on a glass pane.

To the contents of the other beaker is added exactly 3.3

gms. of 50% sodium hydroxide to establish an Na ozsiO ratio differential of 0.015 greater than the other sample. This mixture is stirred thoroughly and to it are then added 4 ml. of a 10% aqueous cobaltous acetate solution and 1 ml. of a 10% aqueous ferric sulfate solution. This mixture is stirred thoroughly and when a 2 temperature rise indicates incipient crystallization, is poured out on a glass pane and allowed to harden.

The first cake, containing no added caustic, is a uniform deep blue color, indicating a siliceous ratio material and that the SiOg:Na O ratio is sufiicient to preclude subsequent turbidity and discoloration of the silicate. The second cake, deliberately causticized with suflicient sodium hydroxide to provide a predetermined alkali-silica ratio variation, develops a yellow ring around its edge within 30 minutes, thereby indicating that the Na O:SiO ratio in the silicate being tested is sufficiently close, i.e., within .015 unit of the true meta ratio to obtain the desired characteristics of the metasilicate and yet avoid subsequent turbidity, gumminess, and product discoloration.

Part B Part C The test described in Part A above is repeated, using metasilicate liquor in which the Na O:SiO ratio is less than 1.0:1.0. In this case, 3.3 gms. of 50% sodium hydroxide is added to the liquor being tested in an amount sufiicient to alter the Na OzsiO ratio a predetermined amount, i.e., .015 unit. The resultant silicate cake develops no yellow ring, thereby indicating the silicateliquor is too siliceous.

In the practice of the invention, as indicated in Example I, When a metasilicate liquor of unknown Na O:SiO ratio and impurity content is to be tested, it

is generally desirable to add separately the metallic color indicator of this invention to an untreated sample of the' liquor and to a deliberately causticized sample, the amount of sodium hydroxide added being that necessary to alter the Na O:SiO ratio in a predetermined amount. This amount generally is dictated by the permissible variation from the metasilicate ratio, i.e., if there may be a :0015 variation, a caustic addition suflicient to alter the Na O:SiO- ratio 0.015 unit, or some multiple thereof, is employed. By such a procedure, the change from the stable color of a satisfactory silicate liquor to the rapid discoloration, characteristic of unsatisfactory silicate liquor, is readily determined and the addition of caustic or silica, or the further purification needed, is indicated.

The practice of this invention is particularly useful in the testing of sodium metasilicate liquors within 10.018 mol unit from the true meta ratio. advantageous in testing silicates having an Na O:SiO ratio within the range from l.000:1.000 to 1.0l8:l.000. While siliceous ratio materials are readily evaluated, silicates having an Na O:SiO ratio substantially in excess of 1.018: 1.000 generally require a longer period of time, e.g., 1 hour or more, to exhibit a color indicative of their alkalinity and impurity content. However, those skilled in the art will recognize, of course, that in many instances the rapidity of the color change is not an important factor and, hence, may utilize the present invention in a wide variety of applications and in testing sili-' cates other than the metasilicates.

The following examples illustrate the use of other color indicators in accordance with the invention.

EXAMPLE II Part A To 170 gms. of an alkaline ratio sodium metasilicate pentahydrate liquor is added 0.534 gm. of

FeSO (NH 6H O dissolved in 5 ml. of water. This mixture is poured on a glass plate and allowed to harden. In 30 minutes the color of the cake has changed from white to a distinct yellow, thereby indicating an Na O:SiO ratio greater Hence, it is highly cause ultimate discoloration of the silicate liquor. A chemical analysis of the liquor indicates that the Na ozSiO ratio is 1.004:1.000.

is observed in this siliceous meta cake, the color remaining a light yellow-green.

Part B 5 To 300 gms. of the same metaliquor used in Part A Part B are added 6 gms. of 50% sodium hydroxide to insure The l' of Part A is repeated, using a siliceous an alkaline ratio material and 0.4 gm. of chromic acetate ratio sodium metasilicate liquor. The cast silicate does d m i 5 1 f Watel; A i P A, h sult nt not fixhibit y change'btlt remains Whitechem" liquor is yellow-green in color. This liquor is then cast i631 analysis O the liquor indicates that the Nazoisioz m on a glass plate, whereupon Within 50 minutes a distinct ra o is 099 1 00 yellow ring appears around the edge of the cake, gradu- EXAMPLE HI ally displacing the green and moving inwardly until the Part A whole alkaline ratlo cake 1s yellow. To 400 gms. of a metasilicate liquor having an Na O: 15 EXAMPLE VI SiO ratio of 0.964 is added ml. of an aqueous solu- Pal! A tion of ferrous sulfate, said solution being prepared by To 400 of Sodium metasilicate liquor having an dissolving 7- of 13650441120 in distilled Water Na O:SiO ratio of 0.977=1.0 is added 0.213 gm. of winch contams Of N/50 H2504 and Subsequently manganous sulfate dissolved in 10 ml. of water containdiluting the mixture to a volume of 250 ml. Theresultm1. of N50 H250? This mixture is cast on a ant silicate is cast a glass Pm and allowgd to glass plate and allowed to harden, the addition of man- The color of the slhcate cake changes from Whlte to a gan'o'us" sulfate causing the siliceous ratio meta liquor blue'gray' to become deep pink in color. This deep pink color Part B persists and does not vary in shade. To a 400 gm. portion of the same metasilicate liquor Part B used in Part A are added 4.8 gms. of GP. sodium hydroxide pellets to provide an alkaline ratio liquor, and To 400 of the Same metaslhcate hquor P Part 5 ml. of the ferrous sulfate solution of Part A. The are added 0213 of n,langanous Sulfate dlssolved resultant silicate mixture is cast on a glass pane and al- 10 of Water contalPmg 1 N/ H2504 lowed to harden. A gray-green color develops, indiand of Sodlum hyflroxlde to an eating an alkaline ratio metasilicate and the presence alkalme ratlo matenal' The ongmal 1 plflk color of sufficient impurities to cause discoloration. caused PY the manganous Sulfate addmon dlsappears as the slllcate hardens when cast on a glass plate. The EXAMPLE IV pink color is replaced by a dark brown to black color r A first appearing at the edge of the cake and gradually To illustrate the effect of using a ferric salt as color moving inwardindicator, 0.365 gm. of Fe (SO dissolved in 10 ml. EXAMPLE VII of distilled water, is added to 280 gms. of a commercial p A sodium metasilicate liquor. During the addition of the ferric sulfate solution to the silicate liquor, the liquor 40 To of slhceous, rano sodlum metaslhcate becomes light pink in color but upon subsequent crystallil ls added 5 mckel acetate sohmon zation becomes white and remains so. Chemical analysis tammg mckel acetat? tetrahydrate' The of the liquor indicates an Na- O:SiO ratio of 0.96:1.0. resultant slhcate hquor 1S ,crystaltlzed and cast glass plate. The cake remains white and does not dis- Part B color with age. To 280 gms. of the same batch of commercial sodium Part B metasilicate liqilor are addFd of aquequs To 300 gms. of the silicate liquor of Part A are sodium hydroxlde, to provide an alkaline ratio material, added 5 m1 of Water containing 0 316 gm of Hi ck el and 0.365 of Fe SO dissolved in 10 ml. of distilled water? This m iirtur is cast on a glass Pane and 50 g tetr-ahydrate and gm? of 50% SOdm-m hyroxide to insure an alkaline ratio material. As 1n Part allowed to harden and in 50 minutes 1s a br1ght yellow A, the liquor is cast on a glass plate and upon casting mcolor' is white in appearance. However, in 16 minutes the EXAMPLE V color changes to cream, the color gradually moving in- Part A ward, and in 42 minutes the entire cake is a cream color. To 300 gms. of metasilicate liquor is added 0.4 gm. The silicate colors produced in accordance with the of chromic acetate dissolved in 5 ml. of water. The reforegoing examples are Summarized in t e following sultant silicate mixture, yellow-green in color, is cast on illustrative table, which table, of Course, is 1101; to be a glass plate and allowed to harden. No color change construed as limiting the invention! Additive NazOzSiOg Initial Color Final Color Ratio 2 a 0 2 {35 55 133 3 3%" 551W oommaom-mio and Fe:(S om.-. {35 33 2 31 555 4-(NH4)fl's 46H2 {gggggg,- 2: reset-mo Egg-gag, ransom gi g OrwzHaoz) {SiliceousZ iggfigg ctreen. MnSO HgO {Alkalm ggm ifi f N (C2Ha02)2-4H2O {smceousuu gg g'g It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. A composition of matter consisting essentially of an aqueous solution of minor amounts of cobaltous acetate tetrahydrate and ferrous acetate.

2. A composition of matter consisting essentially of an aqueous solution of minor amounts of cobaltous acetate tetrahydrate and ferric sulfate.

3. In the testing of alkali metal silicates, the step of adding to the silicate product a minor amount of at least one water-soluble salt of an element of the First Transition Series and thereafter allowing the thus-treated silicate to crystallize and solidify, the color exhibited within a relatively short time after solidification indicating whether ultimate discoloration of the silicate inherently will result.

4. A composition of matter for use in testing sodium metasilicate liquors, said composition consisting essentially of an aqueous solution of a compound of cobalt selected from the group consisting of silicate liquorsoluble bromides, chlorides, nitrates, sulfates, and thiocyanates of cobalt, and a soluble salt of iron selected from the group of ferrous and ferric bromides, chlo rides, nitrates, sulfates, thiocyanates, and the hexahydrate References Cited in the file of this patent Mellors Modern Inorganic Chem., Rev. Ed., by Parkes, G. E. (1951), page 718, Longmans, Green and Co.

Merrill: The Chem. of Silicates, J. of Chem. Education, June 1947, pages 262, 268, 269.

Diamond Chromium Chemicals, Diamond Alkali Co. (1949), pages 11,12 and 27.

F A A marl. 44..

UNITED STATES PATENT OFFICE I @ERTIFICATE OF @ORRECTION Patent N00 2,909,412 October 20-, 1959 Cletus Ea Peeler, Jra

It is hereby certified that error appears in the printed specification of the above numbered patent. requiring correction and' that the said Letters Patent should readas corrected below 0011mm 1, line 37, for "incipent" read incipient column 3, iine 2% far "655] C6" read 65 CE, line 352, for pr0v1d.e read provides s Signed and sealed this 19th day of April 1966,

(SEAL) Attest:

KARL IL, AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

3. IN THE TESTING OF ALKALI METAL SILICATED, THE STEP OF ADDING TO THE SOLICATAE PRODUCT A MINOR AMOUNT OF AT LEAST ONE WATER-SOLUBLE SALT OF AN ELEMENT OF THE FIRST TRANSITION SERIES AND THEREAFTER ALLOWING THE THUS-TREATED SILICATED TO CRYSTALLIZE AND SOLIDIFY, THE COLOR EXHIBITED WITH A RELATIVELY SHORT TIME AFTER SOLIDIFICATION INDICATING WHETHER ULTIMATE DISCOLORATION OF THE SILICATED INHERENTLY WILL RESULT. 